fix(preferences): retain MIDI device labels across dropdown refreshes

Makefile

@@ -612,3 +612,7 @@ test: test-midi-file
 .PHONY: test-configuration-startup
 test-configuration-startup: gui
 	xvfb-run -a -s "-screen 0 1440x960x24" $(PYTHON) tests/integration/test_configuration_startup.py ./$(BUILD_DIR)/xtc
+
+.PHONY: test-gui-midi-labels
+test-gui-midi-labels: $(BUILD_DIR)/test_gui
+	XTC_TEST_MIDI_LABELS_ONLY=1 xvfb-run -a -s "-screen 0 1440x960x24" ./$(BUILD_DIR)/test_gui

docs/ROADMAP.md

@@ -2264,6 +2264,15 @@ Provide device dropdowns and refresh in Preferences, persistent default input/ou
 ### Implementation status
 Implemented: a MIDI preferences tab provides editable source/destination dropdowns, device refresh, input filtering, output channel defaults and optional thru. All choices use the strict shared configuration schema and ~/.xtc.conf. Play/Record restores selected routes; missing devices reject startup without losing choices. Settings roundtrip/invalid-value, GUI discovery/refresh/persistence/missing-device checks and the full GUI suite passed. MIDI help explains host bridge exposure, channel numbering and existing note/CC defaults.
 
+
+Follow-up fix: MIDI dropdown labels now use dialog-owned backing strings because
+FLTK copies menu items but borrows their labels. Menus are cleared before refresh
+or string destruction. The regression test reproduces the previous heap
+use-after-free under AddressSanitizer and verifies both lists, literal names with
+slashes, selection/save, repeated refresh, offline selection retention and None.
+`test-gui-midi-labels`, `test-gui-midi-workflows`, full `test-gui` and the focused
+ASan/UBSan/leak check pass; the GUI application was rebuilt without warnings.
+
 ---
 
 ## Phase 103 — Export Selected Clips as Standard MIDI Files

src/gui/preferences_dialog.hpp

@@ -8,6 +8,8 @@
 #include <FL/Fl_Box.H>
 #include <FL/Fl_Button.H>
 #include <functional>
+#include <cstring>
+#include <utility>
 #include <vector>
 #include <string>
 
@@ -17,11 +19,17 @@ class PreferencesDialog : public Fl_Double_Window {
     std::vector<Fl_Input *> inputs_;
     Fl_Box *message_;
     std::function<std::vector<std::string>(bool)> devices_;
+    std::vector<std::string> midi_names_[2];
     Fl_Input_Choice *midi_input_=nullptr,*midi_output_=nullptr;
     void refresh_devices() {
         for(auto pair:{std::pair<Fl_Input_Choice *,bool>{midi_input_,true},{midi_output_,false}}){
             if(!pair.first)continue;
-            std::string value=pair.first->value();std::vector<std::string> names=devices_ ? devices_(pair.second) : std::vector<std::string>{};
+            std::string value=pair.first->value();
+            // copy() owns the menu array but borrows its label strings.
+            // Release old items before replacing their backing storage.
+            pair.first->menubutton()->clear();
+            auto &names=midi_names_[pair.second ? 0 : 1];
+            names=devices_ ? devices_(pair.second) : std::vector<std::string>{};
             names.insert(names.begin(),"");std::vector<Fl_Menu_Item> items(names.size()+1);
             for(size_t i=0;i<names.size();++i)items[i].text=i ? names[i].c_str() : "(None)";
             pair.first->menubutton()->copy(items.data());pair.first->value(value.c_str());
@@ -89,6 +97,11 @@ class PreferencesDialog : public Fl_Double_Window {
         callback([](Fl_Widget *,void *c){static_cast<PreferencesDialog *>(c)->hide();},this);
         end(); xtc_ui::style(this);
     }
+    ~PreferencesDialog() override {
+        // Destroy borrowed-label menus before the member strings are released.
+        if(midi_input_)midi_input_->menubutton()->clear();
+        if(midi_output_)midi_output_->menubutton()->clear();
+    }
     void run() { show(); while(shown()) Fl::wait(); }
 };
 #endif

tests/integration/test_gui.cpp

@@ -399,8 +399,38 @@ int midi_workflow_tests()
     CHECK(xtc_settings_load(&saved,config.c_str())==XTC_ERR_FORMAT);
     unlink(config.c_str());rmdir(dir);puts("MIDI workflow/configuration GUI checks passed.");return failures ? 1 : 0;
 }
+int midi_device_label_tests()
+{
+    xtc_settings settings{},applied{};xtc_settings_defaults(&settings);unsigned int generation=0;
+    auto names=[&](bool input){return std::vector<std::string>{
+        std::string(input ? "Controller / USB keyboard: MIDI output " : "Synth / USB interface: MIDI input ")+std::string(120,'A'+static_cast<char>(generation)),
+        input ? "Keyboard:out 2" : "Synth:in 2"};};
+    PreferencesDialog dialog(settings,"",[&](const xtc_settings &s){applied=s;return XTC_OK;},names);
+    auto *input=dynamic_cast<Fl_Input_Choice *>(find(&dialog,"Default MIDI input source (next Play)"));
+    auto *output=dynamic_cast<Fl_Input_Choice *>(find(&dialog,"Default MIDI output destination (next Play)"));
+    CHECK(input && output);if(!input || !output)return 1;
+    for(unsigned int pass=0;pass<4;++pass){
+        if(pass){generation=pass;press(find(&dialog,"Refresh MIDI devices"));}
+        // Force reuse of temporary string allocations after enumeration returns.
+        std::vector<std::string> churn(256,std::string(200,'z'));
+        for(auto pair:{std::pair<Fl_Input_Choice *,bool>{input,true},{output,false}}){
+            auto expected=names(pair.second);auto *menu=pair.first->menubutton();
+            CHECK(menu->size()==4 && !strcmp(menu->menu()[0].label(),"(None)"));
+            for(size_t i=0;i<expected.size();++i)CHECK(!strcmp(menu->menu()[i+1].label(),expected[i].c_str()));
+            menu->picked(menu->menu()+1);CHECK(pair.first->value()==expected[0]);
+        }
+        press(find(&dialog,"Apply"));
+        CHECK(applied.midi_input_port==names(true)[0] && applied.midi_output_port==names(false)[0]);
+    }
+    auto selected=std::string(input->value());generation=5;press(find(&dialog,"Refresh MIDI devices"));
+    CHECK(input->value()==selected); // A disconnected device remains remembered.
+    for(auto *choice:{input,output}){choice->menubutton()->picked(choice->menubutton()->menu());CHECK(!*choice->value());}
+    press(find(&dialog,"Apply"));CHECK(!applied.midi_input_port[0] && !applied.midi_output_port[0]);
+    puts("MIDI device dropdown labels/selection/refresh checks passed.");return failures ? 1 : 0;
+}
 int main(int argc, char **argv)
 {
+    if(std::getenv("XTC_TEST_MIDI_LABELS_ONLY"))return midi_device_label_tests();
     if(std::getenv("XTC_TEST_MIDI_WORKFLOWS_ONLY"))return midi_workflow_tests();
     if(std::getenv("XTC_TEST_CREATIVE_ONLY"))return creative_workflow_tests();
     if(std::getenv("XTC_TEST_TRACK_FX_ONLY"))return track_insert_tests();